Field of Endeavor
This invention relates to a method of treating accompanied water from wells produced upon mining natural gas or crude oil from the well of shale gas, oil sand, CBM (coal bed methane), petroleum, or the like.
Brief Description of the Related Art
On mining shale gas, oil sand, CBM (coal bed methane), petroleum, or the like, an aqueous agent solution is sometimes injected as water or steam for digging, for the purpose of improving the output of natural gas or crude oil. As a result, crude oil taken out from an oil stratum contains the aqueous agent solution and underground water containing inorganic ions in the stratum as accompanied water, and the accompanied water is separated from the mined natural gas or crude oil. Since the separated accompanied water contains a salt content, organic materials, suspended solids, and the like, when it is discharged as-is, there is a problem of environmental pollution. Therefore, purification of the water is necessary.
Among the components contained in the accompanied water, soluble silica produces scaling in a process for treating the accompanied water, by adhering to pipes and the inside of apparatuses, and therefore, its removal is an important problem.
In Patent Document 1 (below), a method of removing soluble silica from accompanied water is disclosed, which comprises, after separating oil from accompanied water, adding a magnesium salt and caustic soda to adjust the pH of the accompanied water into the range of 9 to 11, thereby insolubilizing the soluble silica contained in the accompanied water to deposit; then, separating the deposited silica by membrane filtration using a ceramic membrane; thereafter, treating the membrane filtrate, from which the deposited silica has been removed, by a reverse osmosis (RO) membrane, thus, recovering fresh water from the accompanied water by removing residual salts; and evaporating to reuse it.
In Patent Document 2, a method of treating waste water containing silica is disclosed, which comprises adding a treating agent containing at least one kind of the compound selected from iron salts, aluminum salts, and magnesium salts to the water to be treated, depositing flocculates under alkaline conditions at pH 7.5-12, and separating the flocculates to reduce the concentration of silica.